1. Field of the Invention
The present invention relates to a gateway, and particularly, to a gateway for an internet telephone system and software installed in terminals connected to the gateway.
2. Description of the Related Art
FIG. 1 shows an internet telephone system.
An end user of the internet telephone system employs a personal computer (hereinafter referred to as PC) or a telephone. There are four patterns of terminal-to-terminal connection in the internet telephone system:                1) PC→PC (21)        2) PC→gateway→telephone (22)        3) telephone→gateway→PC (23)        4) telephone→gateway→gateway→telephone (24)        
The PCs 11 and 13 must have software such as Netmeeting (registered trademark) to use the internet telephone system. The public telephones 14 and 19 must have the gateways (GWs) 16 and 17 to use the internet telephone system. The gateways 16 and 17 are installed in, for example, provider centers and are connected to telephone networks 15 and 18, to carry out conversion between voice signals and packet signals and connections between the telephone networks 15 and 18 and the Internet 12.
Internet telephone software and gateways have been based on individual specifications devised by their producers. As a result, the use of the internet telephone system is restricted to parties that employ the same software and apparatuses. Recently, VoIP (Voice over the Internet Protocol Forum) started to standardize internet telephone connection among different software and apparatuses and proposed Recommendation H.323 as a standardization base.
ITU-T (International Telecommunication Union Telecommunication Standardization Sector) employs the Recommendation H.323 as an international standard for “Visual Telephone System and Apparatus for Service Quality Unguaranteed LAN” (“ITU-T H Series (related to audio, visual, and multimedia) Recommendations (Part 2)” issued by Zaidan Hojin Sin-Nippon ITU Kyokai). The Recommendation H.323 calls a PC having the above-mentioned software an “H.323 terminal” and the above-mentioned gateway “H.323 gateway” or simply “gateway.”
Japanese Unexamined Patent Publication No. 09-168065 discloses a technique to use the internet telephone system of FIG. 1. This technique arranges a database in a server. The database relates user names, internet protocol (IP) addresses, and telephone numbers to one another. A call contains a receiver IP address. If a PC corresponding to the receiver IP address is unavailable to receive the call, or if internet telephone software installed in the PC is inactive, a telephone number corresponding to the PC is retrieved from the database, and the call is automatically connected to the telephone.
FIGS. 2A and 2B show examples of connection and callback operations in the internet telephone system of FIG. 1. The example of FIG. 2A shows the route 21 or 22 of FIG. 1, and the example of FIG. 2B shows the route 23 or 24 of FIG. 1.
In FIG. 2A, the PC 11 serves as a caller and has an IP address [a.a.a.a], and the PC 13 or gateway 17 serves as a receiver and has an IP address [b.b.b.b]. The PC 11 sends the IP address [a.a.a.a] to the PC 13 or gateway 17. The PC 13 or gateway 17 makes a callback with the IP address [a.a.a.a] of the caller.
In FIG. 2B, the telephone 14 has a telephone number [3000]. When the telephone 14 makes a call, the gateway 16 having an IP address [g.g.g.g] sends the IP address [g.g.g.g] and telephone number [3000] to the PC 13 or gateway 17. The PC 13 or gateway 17 makes a callback with the caller IP address [g.g.g.g] and telephone number [3000].
In these examples, the IP addresses are global IP addresses so that the PCs 11 and 13 and gateways 16 and 17 are uniquely identifiable. The receivers 13 and 17 are able to correctly specify the callers 11 and 14 when making a callback.
As is apparent in the routes 21 and 22, the PC 11, for example, is directly connected to the Internet 12, and therefore, the PC 11 separately keeps a log of internet telephone calls. If a party uses the internet telephone system with many PCs, it is difficult for the party to centrally grasp the use by the PCs of the internet telephone system.
There is a serious shortage of global IP addresses these days. To solve this problem, DHCP (Dynamic Host Configuration Protocol) and private IP addresses are increasingly used. A DHCP server dynamically (instead of fixedly) assigns a global IP address (only one in the world) to a PC when the PC is activated. On the other hand, the private IP addresses are fixedly assigned to PCs in a private LAN and are usable only within the LAN. The private IP addresses are prohibited from being disclosed to the Internet that is public.
As a result, an outside party is unable to call through the internet telephone system a PC in the LAN that employs DHCP or private IP addresses.
In addition, a PC in the LAN that employs private IP addresses is unable to call an outside party through the internet telephone system because the private IP addresses are not allowed to be transmitted as caller addresses to the outside. A PC in the LAN that uses DHCP may call an outside party through the internet telephone system because it is temporarily provided with a global IP address from a DHCP server. The outside party, however, is unable to make a callback because the IP address is temporary.